U.S. patent application number 13/125773 was filed with the patent office on 2012-01-26 for pressure vessel for storing gaseous media under pressure.
This patent application is currently assigned to Daimler AG. Invention is credited to Gerardo Friedlmeier, Thomas Poschmann, Eberhard Schmidt-Ihn, Josef Zieger.
Application Number | 20120018314 13/125773 |
Document ID | / |
Family ID | 41528746 |
Filed Date | 2012-01-26 |
United States Patent
Application |
20120018314 |
Kind Code |
A1 |
Friedlmeier; Gerardo ; et
al. |
January 26, 2012 |
Pressure Vessel for Storing Gaseous Media Under Pressure
Abstract
A pressure vessel for the storage of pressurized gaseous
hydrogen includes a liner which defines an interior for the
accommodation of the gaseous hydrogen and a wrapping encompassing
the liner which gives the pressure vessel its dimensional
stability. In order to prevent a discharge of gaseous hydrogen from
the wrapping of the pressure vessel at a high rate if the pressure
vessel is discharged after a prolonged downtime, the wrapping of
the pressure vessel is designed to be at least partially
gas-permeable, so that the gas penetrating through the liner can
escape continuously through the wrapping of the pressure
vessel.
Inventors: |
Friedlmeier; Gerardo;
(Leinfelden-Echterdingen, DE) ; Poschmann; Thomas;
(Iffeldorf, DE) ; Schmidt-Ihn; Eberhard;
(Darmstadt, DE) ; Zieger; Josef; (Stuttgart,
DE) |
Assignee: |
Daimler AG
Stuttgart
DE
|
Family ID: |
41528746 |
Appl. No.: |
13/125773 |
Filed: |
October 6, 2009 |
PCT Filed: |
October 6, 2009 |
PCT NO: |
PCT/EP2009/007164 |
371 Date: |
July 7, 2011 |
Current U.S.
Class: |
206/.6 |
Current CPC
Class: |
F17C 2201/056 20130101;
Y02E 60/321 20130101; F17C 2205/0305 20130101; F17C 2260/037
20130101; F17C 2270/0184 20130101; F17C 2203/0604 20130101; F17C
2221/012 20130101; F17C 2205/0323 20130101; F17C 2260/042 20130101;
F17C 2203/0607 20130101; F17C 2203/0673 20130101; F17C 2201/0109
20130101; F17C 2205/0397 20130101; F17C 1/06 20130101; F17C
2223/0123 20130101; Y02E 60/32 20130101; F17C 2223/036 20130101;
F17C 2203/0619 20130101 |
Class at
Publication: |
206/6 |
International
Class: |
B65D 83/00 20060101
B65D083/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 25, 2008 |
DE |
10 2008 053 244.4 |
Claims
1. A pressure vessel for storing pressurised gaseous media,
comprising: a liner that defines an interior for accommodation of a
gaseous medium; and a wrapping encompassing the liner that gives
the pressure vessel dimensional stability, wherein the wrapping of
the pressure vessel is at least partially gas-permeable, so that
the gaseous medium penetrates through the liner and escapes from
the pressure vessel through the wrapping.
2. The pressure vessel according to claim 1, wherein the wrapping
of the pressure vessel is at least partially porous and/or provided
with holes (34) which connect the inside of the wrapping to its
outside.
3. The pressure vessel according to claim 1, wherein the wrapping
of the pressure vessel is made of a fibrous material bound with a
resin material, the resin material being at least partially porous
in the set state.
4. The pressure vessel according to claim 1, wherein the wrapping
of the pressure vessel is provided with a coating on its outside,
which is gas-permeable at least in the gas-permeable regions of the
wrapping.
5. A pressure vessel for storing pressurised gaseous media,
comprising: a liner that defines an interior for accommodation of a
gaseous medium; and a wrapping encompassing the liner that gives
the pressure vessel dimensional stability, wherein a gas-permeable
intermediate layer is connected to the outside of the wrapping in
at least one region and is provided between the liner and the
wrapping, so that the gaseous medium penetrates through the liner
and escapes from the pressure vessel through the intermediate
layer.
6. The pressure vessel according to claim 5, wherein the
intermediate layer is at least partially porous.
7. The pressure vessel according to claim 5, wherein a gas
treatment device is provided in a connecting region between the
intermediate layer and the outside of the wrapping.
8. The pressure vessel according to claim 7, wherein the gas
treatment device comprises an oxidising catalyst.
9. The pressure vessel according to claim 7, wherein the gas
treatment device is produced by impregnating the intermediate layer
with a gas treatment medium.
10. The pressure vessel according to claim 7, wherein the
connecting region between the intermediate layer and the outside of
the wrapping is provided in a region of a neck of the pressure
vessel.
11. The pressure vessel according to claim 7, wherein the
connecting region between the intermediate layer and the outside of
the wrapping is provided in a region of a filling and/or discharge
opening of the pressure vessel.
12. The pressure vessel according to claim 2, wherein the wrapping
of the pressure vessel is provided with a coating on its outside,
which is gas-permeable at least in the gas-permeable regions of the
wrapping.
13. The pressure vessel according to claim 3, wherein the wrapping
of the pressure vessel is provided with a coating on its outside,
which is gas-permeable at least in the gas-permeable regions of the
wrapping.
14. The pressure vessel according to claim 6, wherein a gas
treatment device is provided in a connecting region between the
intermediate layer and the outside of the wrapping.
15. The pressure vessel according to claim 8, wherein the gas
treatment device is produced by impregnating the intermediate layer
with a gas treatment medium.
16. The pressure vessel according to claim 8, wherein the
connecting region between the intermediate layer and the outside of
the wrapping is provided in a region of a neck of the pressure
vessel.
17. The pressure vessel according to claim 9, wherein the
connecting region between the intermediate layer and the outside of
the wrapping is provided in a region of a neck of the pressure
vessel.
18. The pressure vessel according to claim 8, wherein the
connecting region between the intermediate layer and the outside of
the wrapping is provided in a region of a filling and/or discharge
opening of the pressure vessel.
19. The pressure vessel according to claim 9, wherein the
connecting region between the intermediate layer and the outside of
the wrapping is provided in a region of a filling and/or discharge
opening of the pressure vessel.
20. The pressure vessel according to claim 10, wherein the
connecting region between the intermediate layer and the outside of
the wrapping is provided in a region of a filling and/or discharge
opening of the pressure vessel.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a national stage of PCT
International Application No. PCT/EP2009/007164, filed Oct. 6,
2009, and claims priority under 35 U.S.C. .sctn.119 to German
Patent Application No. 10 2008 053 244.4, filed Oct. 25, 2008, the
entire disclosures of which afore-mentioned documents are herein
expressly incorporated by reference.
BACKGROUND AND SUMMARY OF THE INVENTION
[0002] The invention relates to a pressure vessel for the storage
of pressurized gaseous media. In particular, it relates to a
pressure vessel of this type, including a liner which defines an
interior for the accommodation of a gaseous medium and a wrapping
encompassing the liner which gives the pressure vessel its
dimensional stability.
[0003] Such generic pressure vessels, which are also referred to as
composite pressure vessels, are known from EP 0 753 700 A1, for
example. They comprise a liner defining an interior for the
accommodation of a gaseous medium and a wrapping encompassing the
liner, which gives the pressure vessel its dimensional stability.
The liner is usually made of a plastic material, while the wrapping
is produced from a fibrous composite material.
[0004] Pressure vessels of this type are for example used as
hydrogen reservoirs in fuel cell systems and can store gaseous
hydrogen at several hundred bars of excess pressure.
[0005] It has been observed that, in a discharge of such composite
pressure vessels after a prolonged downtime, gaseous hydrogen
escapes at a relatively high rate from the wrapping of the pressure
vessel. There is therefore a demand for pressure vessels with a
lower potential risk of hydrogen escape.
[0006] DE 33 08 276 A1 discloses a multilayer pressure vessel for
hot hydrogen, wherein hydrogen which penetrates through the
innermost metal layer of the wall is vented from the space between
the innermost metal layers in order to prevent a hydrogen attack
and/or an embrittlement problem in the outer metal layers of the
wall of the vessel.
[0007] JP 2007-278482 A describes a composite pressure vessel with
an inner tank and an outer tank. In order to protect the outer tank
against attack by hydrogen penetrating through the inner tank and
thereby to improve the durability of the pressure vessel, a
continuous catalyst layer is provided between the inner and outer
tanks, which converts the hydrogen into a stable compound.
[0008] The present invention provides a solution to the problem of
creating a composite pressure vessel of the type referred to above
which excludes any risk to the environment posed by gases escaping
at excessively high rates.
[0009] This problem is solved by providing that an instantaneous
escape of gaseous media at high rates during a discharge of the
pressure vessel after a prolonged downtime is prevented by
discharging gaseous media penetrating through the liner
continuously and therefore at lower rates from the pressure vessel
into the environment. The accumulation of gases penetrating through
the liner in pockets between the liner and the wrapping and their
instantaneous escape at high rates from the pressure vessel into
the environment during a discharge of the pressure vessel as a
result of the separation between liner and wrapping are therefore
avoided.
[0010] According to a first aspect of the invention, a pressure
vessel for the storage of pressurized gaseous media comprises a
liner which defines an interior for the accommodation of a gaseous
medium and a wrapping encompassing the liner, which gives the
pressure vessel its dimensional stability. According to the
invention, the wrapping of the pressure vessel is designed to be at
least partially gas-permeable, allowing the gas penetrating through
the liner to escape from the pressure vessel through the
wrapping.
[0011] This structure of the pressure vessel with an at least
partially gas-permeable wrapping has the result that the gas
penetrating through the liner can be discharged continuously and at
low rates from the pressure vessel into the environment. In this
way, the accumulation of the gas penetrating through the liner
between the liner and the wrapping, and its instantaneous escape at
high rates from the pressure vessel into the environment during a
discharge of the pressure vessel, are prevented.
[0012] In a variant of the invention, the wrapping of the pressure
vessel is designed to be at least partially porous. The wrapping of
the pressure vessel may, for example, be made of a fibrous material
bound with a resin material, the resin material being at least
partially porous in the set state.
[0013] Alternatively or in addition, the wrapping of the pressure
vessel is provided at predetermined points with holes which connect
the interior of the wrapping to its outside.
[0014] In a further development of the invention, the wrapping of
the pressure vessel is provided on its outside with a coating
(e.g., layer of paint) which is likewise designed to be
gas-permeable at least in the gas-permeable regions of the
wrapping.
[0015] According to a second aspect of the invention, a pressure
vessel for the storage of pressurized gaseous media comprises a
liner which defines an interior for the accommodation of a gaseous
medium and a wrapping encompassing the liner, which gives the
pressure vessel its dimensional stability. According to the
invention, a gas-permeable intermediate layer is provided between
the liner and the wrapping, this being connected to the outside of
the wrapping in at least one region, so that the gas penetrating
through the liner can escape from the pressure vessel through the
intermediate layer.
[0016] This structure of the pressure vessel with an at least
partially gas-permeable intermediate layer between the liner and
the wrapping has the result that the gas penetrating through the
liner can be discharged continuously and at low rates from the
pressure vessel into the environment. In this way, the accumulation
of the gas penetrating through the liner between the liner and the
wrapping, and its instantaneous escape at high rates from the
pressure vessel into the environment during a discharge of the
pressure vessel, are prevented.
[0017] In a variant of the invention, the intermediate layer is at
least partially porous.
[0018] In a further development of the invention, a gas treatment
device which may, for example, be formed by impregnating the
intermediate layer with a gas treatment medium is provided in the
connecting region between the intermediate layer and the outside of
the wrapping.
[0019] The gas treatment device may for example comprise an
oxidising catalyst. If the gaseous medium stored in the pressure
vessel is hydrogen, the hydrogen flowing through the liner and
through the intermediate layer is oxidized to water by the
oxidizing catalyst and can be discharged without endangering the
environment.
[0020] In a further development of the invention, the connecting
region between the intermediate layer and the outside of the
wrapping is provided in the region of a neck of the pressure
vessel. This may be the region of a filling and/or discharge
opening of the pressure vessel.
[0021] The above and further features and advantages of the present
invention are understood more easily from a perusal of the
following description of preferred embodiments with reference to
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0022] FIG. 1 is a diagrammatic sectional view of a composite
pressure vessel according to the present invention;
[0023] FIG. 2 is an enlarged part-section of a conventional
composite pressure vessel before its discharge;
[0024] FIG. 3 is an enlarged part-section of a conventional
composite pressure vessel after its discharge;
[0025] FIG. 4 is an enlarged part-section of a composite pressure
vessel according to a first embodiment of the invention before its
discharge;
[0026] FIG. 5 is an enlarged part-section of a composite pressure
vessel according to a first embodiment of the invention after its
discharge; and
[0027] FIG. 6 is a diagrammatic sectional view of a composite
pressure vessel according to a second embodiment of the present
invention.
DETAILED DESCRIPTION OF THE DRAWING FIGURES
[0028] The present invention is described below with reference to a
pressure vessel for the storage of gaseous hydrogen at a pressure
of, e.g., 700 bar, which may be used, for example, in fuel cell
systems. The invention is, however, in no way restricted to this
particular gaseous medium, this particular excess pressure in the
interior of the pressure vessel and this particular
application.
[0029] With reference to FIG. 1, the basic structure of a composite
pressure vessel to which the present invention can be applied is
described in greater detail below.
[0030] The composite pressure vessel 10 is formed from a liner 12
which defines an interior 14 for the accommodation of gaseous
hydrogen. A plastic material may for example be used for the
production of the liner 12. The liner 12 is surrounded by a
wrapping 16 which may, for example, be made of a fibrous composite
material such as resin-impregnated carbon fibers and which gives
the pressure vessel 10 the necessary dimensional stability. The
materials for the production of the liner 12 and the wrapping 16
are, however, not restricted to those mentioned above. In the same
way, the invention is not restricted to a specific form of the
wrapping 16 (e.g., axial and/or tangential and/or angled winding
direction of the fibers) and to a specific thickness of the liner
12 and the wrapping 16. As the basic structure of the pressure
vessel is known to the expert from prior art, the design of an
embodiment fulfilling specific requirements (e.g., type of gas,
pressure, application, etc.) will not pose any problems for him or
her.
[0031] In the embodiment of FIG. 1, the pressure vessel 10 has two
neck regions (on top and at the bottom in FIG. 1), each of which is
provided with an opening 22 sealed by a neck piece 18 and 20,
respectively. In the opening 22 which is not sealed by a neck piece
(on top in the figure), a valve 24 may be provided. The present
invention is not restricted to a specific design of the neck pieces
18, 20. In addition, the two neck regions of the pressure vessel 10
may be provided with pole caps for the additional stabilization of
the pressure vessel 10. The pressure vessel 10 may optionally be
provided with two openings 22 fitted with valves 24. The shape of
the pressure vessel 10 is moreover not restricted to that with two
neck regions as shown in FIG. 1.
[0032] A coating 26, for example, a layer of paint, is further
applied to the outside of the wrapping 16.
[0033] The problems of hydrogen escape from a conventional pressure
vessel are explained below with reference to FIGS. 2 and 3.
[0034] In the interior 14 of the pressure vessel 10, gaseous
hydrogen may, for example, be stored at a pressure of approximately
700 bar. In the course of time, a certain amount of this hydrogen
is diffused through the liner 12 (see arrow 28 in FIG. 2). This
gaseous hydrogen which has penetrated through the liner 12 largely
accumulates in pockets 30 between the liner 12 and the wrapping 16.
A small proportion of this hydrogen may reach the environment
through pores or holes 32 in the wrapping 16. A free access of this
accumulated hydrogen to the few small holes 32 in the wrapping is
greatly impeded by a macroscopically flush contact between the
wrapping 16 and the liner 12 at high pressure in the interior 14 of
the liner 12.
[0035] After a prolonged downtime of the pressure vessel 10, the
hydrogen in the pockets 30 between the liner 12 and the wrapping 16
causes a build-up of pressure which may in extreme cases result in
a deformation of the liner 12.
[0036] If the pressure vessel 10 is then discharged after a
prolonged downtime, or if a defined quantity of hydrogen is taken
from the interior 14, so that the pressure in the interior 14 is
reduced significantly, an excess pressure is created by the
hydrogen accumulated in the pockets 30 between the liner 12 and the
wrapping 16. As illustrated in FIG. 3, this excess pressure
separates the liner 12 from the inside of the wrapping 16 and may
also cause a deformation of the liner 12. This separation (see
double-headed arrow in FIG. 3) creates a flow path for the gaseous
hydrogen from the pockets 30 to the pores/holes 32 and thus to the
outside of the wrapping 16, allowing hydrogen which has penetrated
through the liner 12 to escape from the pressure vessel 10.
[0037] If the pressure vessel 10 is then discharged after a
prolonged downtime, the hydrogen diffused through the liner
instantaneously flows from the pressure vessel 10 at a
comparatively high rate.
[0038] In order to prevent a risk to the environment posed by the
hydrogen escaping from the pressure vessel 10 at a high rate, the
present invention proposes that the pressure build-up between the
liner 12 and the wrapping 16 after a prolonged downtime of the
pressure vessel 10, which has been described above, should be
avoided. For this purpose various measures are taken within the
scope of the present invention.
[0039] A first embodiment of a pressure vessel according to the
invention is explained below with reference to FIGS. 4 and 5.
[0040] Like the conventional pressure vessel, the pressure vessel
10 of this embodiment comprises a liner 12 which defines an
interior 14 for the accommodation of a gaseous medium and a
wrapping 16 encompassing the liner 12. In this design of the
pressure vessel 10, during prolonged downtimes a high pressure in
the interior 14 likewise causes the diffusion of a small quantity
of hydrogen through the liner 12 (see arrows 28 in FIG. 4), the
hydrogen initially accumulating in pockets 30 between the liner 12
and the wrapping 16.
[0041] In contrast to the conventional composite pressure vessels
described above, however, the wrapping of the pressure vessel 10 of
this embodiment is designed to be at least partially gas-permeable.
For this purpose, the wrapping 16 may for example be porous.
Alternatively or in addition, the wrapping 16 is provided at
predetermined points with holes 34 which connect the interior of
the wrapping 16 to its outside. In this way, the gaseous hydrogen
penetrating through the liner 12 can be discharged continuously and
at low rates through the wrapping 16 to the outside. Compared to
the instantaneous release of the hydrogen at a high rate, the
potential risk to the surroundings of the pressure vessel 10 posed
by the escaping gaseous hydrogen is noticeably reduced.
[0042] Even if the liner 12 in this case separates slightly from
the wrapping 16 as the pressure vessel 10 is discharged, creating
flow paths between individual pockets 30 as shown in FIG. 5, large
quantities of hydrogen are no longer released in this state,
because the hydrogen has already been discharged evenly through the
wrapping 16 over a long period of time and has not been able to
build up any significant pressure between the liner 12 and the
wrapping 16.
[0043] The wrapping 16 is designed to be gas-permeable at least in
certain regions. In exemplary embodiments of the invention,
however, the wrapping is designed to be gas-permeable substantially
across all of its regions.
[0044] If, as FIG. 1 shows, the wrapping 16 is coated with a layer
of paint 26 or the like, this layer of paint 26 will have to be
gas-permeable as well in this embodiment. This applies at least to
the regions in which the wrapping 16 is designed to be
gas-permeable.
[0045] The porous wrapping 16 may for example be structured as
follows. The wrapping 16 essentially consists of a fibrous
composite material which may for example be made up from carbon
fibers which give the wrapping its inherent compressive strength
and of a resin for binding the carbon fibers. This resin has to be
at least partially porous. The strength and stability under
pressure of the wrapping 16 as a whole will nevertheless have to be
ensured. The resin used for binding does not make any significant
contribution to the stability of the pressure vessel 10 under
pressure; the deciding factor is the carbon fiber bond.
[0046] To produce the porous wrapping 16, a resin may be used
which, owing to high inner stresses, forms a sufficient number of
micro-cracks in the setting process. These micro-cracks must,
however, not result in a complete disintegration of the wrapping
16. In addition, the micro-cracks have to form a continuous
connection through the entire wrapping 16, as they are required for
the removal of the hydrogen into the environment.
[0047] The same conditions apply to any outer layer of paint 26
which may be provided. This can also be produced using the method
described above and has to meet the same conditions with respect to
hydrogen removal.
[0048] The provision of tailor-made holes 34 in sufficient numbers
at points previously determined does not require any detailed
explanation. In principle, any suitable methods may be used.
[0049] The gas-permeability of the wrapping 16 obviously varies
with the gas in the interior 14 of the pressure vessel 10.
Depending on the type of gaseous medium stored in the pressure
vessel 10, the gas permeability characteristics, e.g., porosity
and/or holes 34, will have to be adapted accordingly.
[0050] A second embodiment of a composite pressure vessel according
to the present invention is described in greater detail below with
reference to FIG. 6.
[0051] Like the conventional pressure vessel, the pressure vessel
10 of this embodiment comprises a liner 12 which defines an
interior 14 for the accommodation of a gaseous medium and a
wrapping 16 encompassing the liner 12. In this design of the
pressure vessel 10 as well, during prolonged downtimes a high
pressure in the interior 14 causes the diffusion of a small
quantity of hydrogen through the liner 12.
[0052] In contrast to the conventional composite pressure vessels
described above, the pressure vessel 10 of the embodiment shown in
FIG. 6 is provided with a gas-permeable intermediate layer 36
between the liner 12 and the wrapping 16. This intermediate layer
36 may be connected to the outside of the wrapping 16, i.e., to the
environment of the pressure vessel 10, in the neck regions
(right-and left-hand side in FIG. 6) of the pressure vessel 10. In
this way, the gaseous hydrogen which penetrates through the liner
12 can be discharged into the environment through the intermediate
layer 36 continuously and at low rates. Compared to the
instantaneous release of the hydrogen at a high rate, the potential
risk to the surroundings of the pressure vessel 10 posed by the
escaping gaseous hydrogen is noticeably reduced.
[0053] The wrapping 16 itself may be gas-tight like in conventional
pressure vessels and optionally provided with a coating 26, for
example a layer of paint. The intermediate layer 36 provided
according to the invention is, for example, at least partially
porous.
[0054] In addition, a gas treatment device 38 is provided in the
connecting regions between the intermediate layer 36 and the
surroundings of the pressure vessel 10, i.e., in the embodiment of
FIG. 6 in the neck region of the pressure vessel 10 at the filling
and/or discharge opening 22. This gas treatment device 38 may, for
example, be produced by impregnating the porous intermediate layer
36 with a suitable gas treatment medium.
[0055] If gaseous hydrogen is to be stored in the interior 14 of
the pressure vessel 10, this gas treatment device 38 may comprise
an oxidizing catalyst which oxidizes the hydrogen in the connecting
regions described above into water. The water produced in this way
is discharged as a liquid or vapor while hydrogen flows after it
through the intermediate layer 36. Any risk to the environment of
the pressure vessel 10 posed by the discharge of hydrogen is
completely avoided in this embodiment.
[0056] The oxidative catalytically-acting part 38 of the porous
intermediate layer 36 is restricted to the region where the
intermediate layer 36 emerges into the environment of the pressure
vessel 10, where hydrogen would be discharged without the gas
treatment device 38. The catalytically-acting region 38 may for
example be produced by impregnating the porous intermediate layer
36 with a liquid which contains the catalyst in a dissolved or
suspended form. By means of a thermal after-treatment of this
impregnated region 38, the activity of the catalyst can be
increased further. If the porous intermediate layer 36 has already
been applied to the liner 12, such a thermal after-treatment has
obviously to be restricted to temperatures which will not damage
the liner 12.
[0057] As the oxidizing catalyst 38 is provided in the connecting
region of the normal hydrogen outlet into the environment, there is
sufficient access for the oxygen required for catalytic
oxidation.
[0058] As the hydrogen penetrating through the liner 12 is
discharged continuously, excess pressure does not develop between
the liner 12 and the wrapping 16 while the pressure vessel is
discharged and pressure is reduced in the interior 14 of the liner,
so that an uneven deformation of the liner 12 is avoided.
[0059] In this context, a method for the application of the porous
intermediate layer 36 to the liner 12 has to ensure that the free
permeability of the porous intermediate layer 36 to hydrogen is
maintained up to the catalytically-acting region 38 both in this
process and during the subsequent application of the wrapping 16,
in order to ensure that the hydrogen penetrating through the liner
12 if fed to the gas treatment device 38.
[0060] The same applies to the oxidising catalyst 38 at the free
end of the porous intermediate layer 36, which may, for example, be
produced by impregnation, in order to ensure an unimpeded discharge
of the water produced in the catalyst 38 to the environment.
[0061] The foregoing disclosure has been set forth merely to
illustrate the invention and is not intended to be limiting. Since
modifications of the disclosed embodiments incorporating the spirit
and substance of the invention may occur to persons skilled in the
art, the invention should be construed to include everything within
the scope of the appended claims and equivalents thereof.
* * * * *